Oh gosh - I so empathise. It's hard finding the reason to do it if you don't feel that you're worth it. But you are worth it, and you will feel better for it if you can lose some more.
I'm willing to bet that your knees ache? And your back? I know they do because mine do too - because of the weight. I'm really looking forward to being able to move more easily when I'm a couple of stone (well, OK - several stone) lighter, and putting less stress on my joints. I'm also willing to bet that you get out of breath easily, and struggle to run for a bus ... because I do too. It will be so nice when we don't even have to think about it - we can just run and not struggle.
We are putting our health at risk - I know it, and you know it too. I want to be around for my daughter for a long time yet; if I don't lose some weight I will be dead of a heart attack before I'm 45. I don't want that, and I'm sure you don't want that either. Plus there's the increased risk of diabetes, blood pressure problems, so many other things that are exacerbated by being very overweight. We deserve not to have to be thinking about things like that, and our children (and those children we don't have yet) deserve to have us around for a long time. I'm not doing this for me - I don't value myself enough yet ... but I value my daughter so much that I can't measure it, and I'm doing this for her.
I'm looking forward to being able to put pretty clothes on in the summer, and not having to hide behind baggy t-shirts and thick trousers. I'm looking forward to catching sight of myself in the mirror in a shop and thinking, "Who's that lovely creature?" OK, so I can dream
... but if I can shift this weight it will be a reality. It's not going to happen if I don't try ... it would be nice, but it won't happen. The only person who can control what I put in my mouth is me.
God, I sound like a sanctimonious old prig, don't I 
I wonder how we could work on our self-esteem - because I don't know about you, but that's partly where my weight comes from, and it's also partly the reason why I struggle to shift weight.